U.S. patent application number 12/744409 was filed with the patent office on 2010-09-30 for network entry and device discovery for cognitive radio networks.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS, N.V.. Invention is credited to KIRAN CHALLAPALI, JIANFENG WANG.
Application Number | 20100246434 12/744409 |
Document ID | / |
Family ID | 40551376 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100246434 |
Kind Code |
A1 |
WANG; JIANFENG ; et
al. |
September 30, 2010 |
NETWORK ENTRY AND DEVICE DISCOVERY FOR COGNITIVE RADIO NETWORKS
Abstract
A device (400) scans and classifies each channel within a
spectrum of channels (215-270) as being occupied or unoccupied
(255), and, if occupied, whether it is occupied by a primary user
(240), a secondary user (230), or an unknown user (260). As a
secondary device (400), transmissions are avoided on channels
occupied by primary users (490). The device selectively joins an
existing network of secondary devices, or establishes a new network
on an unoccupied channel (125), based on the quality of service
(QoS) that the channel can provide and/or other factors. If the
device is paired with a target device (115), the paired device
advertises itself on a selected channel (345-360) for a period that
is at least as long as the time required to scan all channels, to
facilitate discovery in the event that the target device is also in
a search mode. The advertising duration randomly alternates (345)
among integer multiples of the scan duration.
Inventors: |
WANG; JIANFENG; (OSSINING,
NY) ; CHALLAPALI; KIRAN; (NEW CITY, NY) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS,
N.V.
EINDHOVEN
NL
|
Family ID: |
40551376 |
Appl. No.: |
12/744409 |
Filed: |
November 24, 2008 |
PCT Filed: |
November 24, 2008 |
PCT NO: |
PCT/IB08/54929 |
371 Date: |
May 24, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60990312 |
Nov 27, 2007 |
|
|
|
Current U.S.
Class: |
370/253 ;
370/255 |
Current CPC
Class: |
H04W 72/044 20130101;
H04W 48/16 20130101 |
Class at
Publication: |
370/253 ;
370/255 |
International
Class: |
H04L 12/26 20060101
H04L012/26; H04L 12/28 20060101 H04L012/28 |
Claims
1. A method comprising: selecting (215) a channel of a plurality of
available channels; monitoring (220) the channel to determine a
classification of the channel as being one of: used by a primary
user (240), used by one or more secondary users (230), used by an
unknown class of user (260), and unused (255); storing (440) the
classification of the channel, and repeating (270) the selecting
and monitoring until each of the plurality of available channels
has been classified.
2. The method of claim 1, wherein determining (230) the channel as
being used by one or more secondary users includes detecting one or
more beacon signals.
3. The method of claim 2, wherein determining (240) the channel as
being used by a primary user (490) includes detecting features that
are characteristic of the primary user.
4. The method of claim 3, wherein determining (260) the channel as
being used by an unknown class of user includes detecting energy
above a threshold that does not correspond to one or more beacons
and does not correspond to the features that are characteristic of
the primary user (490).
5. The method of claim 1, including informing a user of the
classifications of one or more of the plurality of available
channels.
6. The method of claim 1, including (125) if at least one channel
is being used by one or more secondary users, joining a network on
the at least one channel.
7. The method of claim 6, wherein joining the network is based on
one of a user directive, association with at least one of the one
or more secondary users, association with the network, a QoS
characteristic of the network, and an amount of traffic on the
network.
8. The method of claim 1, including if at least one channel is
unused, transmitting an advertising beacon on the at least one
channel (125).
9. The method of claim 1, including if the channel is being used by
one or more secondary users, storing (440) an identification of
each of the one or more secondary users (235) on the channel.
10. The method of claim 9, including accessing the stored
identification of each secondary user to locate a target user
(335), and joining a network on the channel associated with the
identification of the target user (375).
11. The method of claim 1, including receiving an other
classification of a channel of the plurality of channels from one
of the secondary users, and modifying the classification of the
channel based on the other classification.
12. The method of claim 1, including transmitting the
classification of one or more of the plurality of channels to one
or more of the secondary users.
13. A method comprising: scanning (330) a plurality of channels for
a beacon of a target device for a scan duration, and if (335) the
beacon of the target device is not detected: randomly selecting
(345) an advertise duration from among a set of predefined
durations, transmitting (350) an advertising beacon on a select
channel (340) during the advertise duration, and if (355) a
response to the advertising beacon is not received from the target
device: repeating (365) the scanning (330) of one or more of the
plurality of channels and transmitting (350) of the advertising
beacon at another select channel; otherwise: establishing
communication (375) with the target device.
14. The method of claim 13, including terminating (365) the
repeating, and transmitting the advertising beacon on one of the
plurality of available channels (370).
15. The method of claim 14, wherein terminating (365) the repeating
is based on at least one of a predefined time limit, a predefined
number of repetitions, a role of the target device, and a user
input.
16. The method of claim 13, wherein selecting (340) the select
channel includes selecting the select channel from among channels
of the plurality of channels that do not exhibit use by a primary
user.
17. The method of claim 13, wherein the repeating (365) includes
storing (440) a record of each scanned channel being one of used by
a primary user (240), used by one or more secondary users (230),
used by an unknown class of user (260), and unused (255).
18. The method of claim 13, wherein values of the set of predefined
durations are dependent upon the scan duration (345).
19. The method of claim 18, wherein values of the set of predefined
durations include the scan duration and twice the scan duration
(345).
20. The method of claim 13, wherein the one or more of the
plurality of channels are selected (340) from among channels at
which a primary user was not detected during the scanning.
21. A method of network discovery by a device (400) among a
plurality of channels having primary (490) and secondary (400)
users, comprising: if (115) the device is paired with a target
device: if (315) the device is not a master of a master-slave pair:
scanning (330) a plurality of channels for a beacon of the target
device for a scan duration, and if (335) the beacon of the target
device is not detected: transmitting (350) an advertising beacon on
a select channel (340) during an advertise duration (345-360), and
if (355) a response to the advertising beacon is not received from
the target device, repeating (365) the scanning (330) of one or
more of the plurality of channels and transmitting (350) of the
advertising beacon at another select channel (340); otherwise, if
(315) the device is the master of the master-slave pair,
transmitting (390) an advertising beacon on a select channel (385);
and establishing (145) communication with the target device;
otherwise, if (115) the device is not paired with the target
device: selecting (215) a channel of the plurality of available
channels; monitoring (220) the channel to determine a
classification of the channel based at least upon whether a primary
or secondary user is detected (230, 240), storing (440) the
classification of the channel, and repeating (270) the selecting
(215) and monitoring (220) until each of the plurality of available
channels has been classified; and selecting (125) a select channel
from among one or more of the plurality of channels at which at
least one secondary user is detected, and establishing
communication (125) with the at least one secondary user on the
select channel.
22. An apparatus (400) comprising: a receiver (410); a transmitter
(430); a controller (450) that is configured to control the
receiver to tune to each channel of a plurality of channels; a
channel classifier (420) that is configured to determine a
classification of each channel as being one of: used by a primary
user (240), used by one or more secondary users (230), used by an
unknown class of user (260), and unused (255); and a memory (440)
that is configured to store the classification of each channel,
wherein the controller (450) is configured to control the
transmitter (430) to selectively effect each of (125): joining a
network on a select channel that is classified as being used by one
or more secondary users, and establishing a network on a select
channel that is classified as being unused.
23. The apparatus (400) of claim 22, wherein the controller (450)
is configured to selectively join (125) the network based on one of
a user directive, association with at least one of the one or more
secondary users, association with the network, a QoS characteristic
of the network, and an amount of traffic on the network.
24. An apparatus (400) comprising: a receiver (410), a transmitter
(430), and a controller (450) that is configured to: control the
receiver (410) to scan (330) each of a plurality of channels for a
beacon of a target device for a scan duration, and if (335) the
beacon of the target device is not detected: randomly select (345)
an advertise duration from among a set of predefined durations, and
control the transmitter (430) to transmit (350) an advertising
beacon on a select channel (340) during the advertise duration
(345-360), and if (355) a response to the advertising beacon is not
received from the target device, repeating (365) the control of the
receiver (410) to scan (330) one or more of the plurality of
channels and the control of the transmitter (430) to transmit (350)
the advertising beacon at another select channel (340); otherwise,
if (335, 355) the target device is detected, control the
transmitter (430) and receiver (410) to establish communication
(375) with the target device.
25. The apparatus of claim 24, wherein the controller (350) is
configured to terminate (365) the repeating of the scan (330) of
the one or more of the plurality of channels based on at least one
of a predefined time limit, a predefined number of repetitions, a
role of the target device, and a user input; and transmitting (125)
the advertising beacon on one of the plurality of available
channels.
Description
[0001] This invention relates to the field of cognitive radio
communications, and in particular to a method and system for
network entry and device discovery for local/personal area
unlicensed operation over TV bands.
[0002] Cognitive radio is a communication scheme in which a device
monitors licensed channels for activity, and establishes
communications only on an inactive channel. It is a particularly
viable solution for providing unused communications bandwidth to
local area communication networks, such as home networks. Such home
networks are commonly used to allow devices and appliances within a
household to communicate and interact with each other, generally
under a user's direct or pre-programmed command. Such
communications may range from a user command to preheat an oven, to
the exchange of audio/visual information among cameras, recorders,
displays, and the like.
[0003] Because many of the devices that may communicate over a
local network are mobile, and because the same device may be a
member of different networks at different locations, or even at the
same location, and because the operating channel of the network may
vary depending upon the activity on the available channels, the
configuration, membership, and even the very existence of such a
network is highly dynamic. Accordingly, techniques must be provided
to enable a device to discover the presence of such dynamic
networks, join an established network, and/or establish a new
network on an available channel.
[0004] A number of different techniques have been proposed to
enable device discovery and network entry in dynamic cognitive
networks, generally based on random or exhaustive search techniques
with minimal regard to efficiency and reliability. Consider, for
example, the time required for two devices to find each other and
establish (unlicensed) operation over conventional television
broadcast bands. For the purposes of this disclosure, the
authorized user of the band (i.e. the licensed broadcaster) is
termed the primary user of the band/channel, and all other
communicating devices on the band are termed secondary users.
Unlicensed operation over TV bands requires a device to make sure
there is no primary user before it attempts communication on a
channel, which may take a long time. Moreover, a seeking device can
not generally presuppose a pre-assigned channel where a target
device or set of devices may be found, given the time-varying and
unpredictable nature of channel occupancy. Typically, the number of
available TV bands is about 30, and, even if the target device is
actively transmitting on a single channel during the search period,
the time to locate the target can amount to a few seconds, and this
time will increase substantially if the target device is also
searching among these 30 channels, and not actively transmitting on
a single channel.
[0005] It would be advantageous to provide a protocol that
facilitates efficient device discovery and network entry in a
dynamic network environment. It would also be advantageous to
provide a protocol that facilitates efficient peer-to-peer device
discovery in a dynamic network environment.
[0006] These advantages, and others, can be realized by a method
and system wherein a device scans and classifies each channel
within a spectrum of channels, then selectively joins an existing
network or establishes a new network based on the determined
channel classifications, and based on the quality of service (QoS)
that the channel can provide and/or other factors. If the device is
paired with a target device, the scanning is terminated when the
target device is found. If the target device is not found, the
paired device advertises itself on a selected channel for a period
that is at least as long as the time required to scan all channels,
to facilitate discovery in the event that the target device is also
in a search mode. The advertising duration preferably randomly
alternates among integer multiples of the scan duration.
[0007] The invention is explained in further detail, and by way of
example, with reference to the accompanying drawings wherein:
[0008] FIG. 1 illustrates an example flow diagram for device
discovery and network entry.
[0009] FIG. 2 illustrates an example flow diagram for scanning and
classifying channels.
[0010] FIG. 3 illustrates an example flow diagram for pair target
discovery.
[0011] FIG. 4 illustrates an example system of dynamically
re-locatable secondary user devices operating in an environment of
primary users.
[0012] Throughout the drawings, the same reference numeral refers
to the same element, or an element that performs substantially the
same function. The drawings are included for illustrative purposes
and are not intended to limit the scope of the invention.
[0013] In the following description, for purposes of explanation
rather than limitation, specific details are set forth such as the
particular architecture, interfaces, techniques, etc., in order to
provide a thorough understanding of the present invention. However,
it will be apparent to those skilled in the art that the present
invention may be practiced in other embodiments, which depart from
these specific details. For purposes of simplicity and clarity,
detailed descriptions of well-known devices, circuits, and methods
are omitted so as not to obscure the description of the present
invention with unnecessary detail.
[0014] As discussed above, the invention addresses devices and
networks that are dynamically re-locatable among a variety of
possible channels. In a typical embodiment, the possible channels
are channels that are generally allocated or licensed to primary
users, such as television broadcasters, but the actual occupancy of
each channel varies. For example, due to the likelihood of
interference, the allocation of television channels to broadcasters
in a given area is restricted to every-other channel, leaving half
of the channels in the available spectrum empty. In other
environments, the occupancy of a channel by a primary user varies
with time. Dynamically re-locatable networks can take advantage of
the inefficiently utilized spectrum by establishing themselves on
unused channels. For ease of understanding, the invention is
presented using a one-to-one correspondence between defined
channels and the utilization of the channel by a secondary user
network. One of skill in the art will recognize, however, that
multiple networks may be supportable within one channel, or,
multiple channels may be required to support one network, without
departing from the intent and scope of this invention.
[0015] FIG. 1 illustrates an example flow diagram for device
discovery and network entry. The search process starts at 110. If,
at 115, the device is not part of a pair, such as a master-slave
pair, or a peer-to-peer pair, a general channel search and
classification is performed, at 120. As discussed further below,
each channel in the search spectrum is classified as being
unoccupied, or occupied by a primary user, secondary user(s), or an
unknown class of user. The primary user is an authorized/licensed
user of a channel; the searching device, being a secondary user of
the channel, is configured to avoid initiating transmissions on any
channel that is classified as a primary channel. In like manner,
the searching device is also configured to avoid transmitting on a
channel being used by an unknown class of user. As discussed
further below, the protocol used by secondary users preferably
includes a means of self-identification by each device on the
network, or at least an identification of the particular network.
In a typical beacon-based protocol, the beacon signal that is
broadcast by each device in a network is preferably configured to
include a device identifier, and optionally, a network
identifier.
[0016] At 125, the device either joins an existing network on a
channel being used by other secondary users, or establishes a new
network on an unused channel. Any of a variety of protocols may be
used to effect the establishment of a new network, and/or to
control access to the network and subsequent communication among
members of the network. In a beacon-based system, a device
establishes a new network by broadcasting a device beacon that
includes the aforementioned device identifier and an identifier of
the network, or type of network, as an invitation to other devices
to join the network. Membership in the network may be open or
selective, depending upon the parameters established when the
network is created.
[0017] The choice of whether to establish a new network or to join
an existing network is generally based on a variety of factors,
including the characteristics of the particular device, as well as
the characteristics of the available networks and channels. In an
example embodiment, a rules-based algorithm is used to effect the
selection.
[0018] An example set of rules for determining whether to join a
discovered network includes, for example, establishing a connection
with the network if the device recognizes an association with one
or more of the secondary users in the network, or an association
based on an identifier of the network. For example, the device may
be a cell phone that has established an association with devices in
a user's home network; whenever the cell phone is brought back into
the vicinity of one or more of these devices, the cell phone will,
by default, join the newly discovered/re-discovered network of
these devices. Similarly, if an association is not recognized, or
if associations to multiple networks are recognized, the selection
of the network to join may be based on each available network's
ability to provide a desired quality of service (QoS), including an
assessment of the available throughput based on the monitoring of
current traffic on each channel. If the device includes a display,
the available networks may be displayed for direct selection by the
user.
[0019] The choice of joining or establishing a network may also
depend upon the particular type or class of device. If, for
example, the device is one that typically provides control of other
devices, such as a user's PDA, the default may be to establish a
new network unless it is clear that an existing network is an
appropriate network to join, based on either the presence or
absence of other types of devices on the network. For example, a
controlling-class device may avoid joining a network that includes
another controlling-class device. Conversely, a controlled-class
device, such as a household appliance, may be configured to give
preference to any network that includes a controlling-class
device.
[0020] One of skill in the art will recognize that other selection
schemes may also be used. For example, the device may be configured
to use a scoring system based on the membership of each network and
the quality of service available. Based on the score, the device
may be configured to select the network having the highest score,
or establish a new network if the highest score is below some
minimum threshold.
[0021] When a device joins a network, a setup process is generally
initiated, wherein the device and network share information that
facilitates subsequent operations of the network. In a basic setup,
for example, the device may be assigned an IP-address by the
network, or the device may inform the network of its predefined
IP-address. In a home or office network, the device may inform the
network of its capabilities and may request allocation of services
or features from the network. Other devices in the network may
modify their configuration to take advantage of the capabilities
provided by the new device, or may advise the new device of their
capabilities.
[0022] In a preferred embodiment, the devices are configured to
share their assessments of the current channel, as well as other
assessed channels. Of particular import, the devices are configured
to maintain a consistent list of channels upon which primary users
have been detected. Some devices, for example, may be in a `fringe`
area of a primary user's broadcast, and may not have detected the
primary user's presence. Each device on the network preferably
updates its classifications based on the determined classifications
by other devices. Depending upon the particular environment, the
network may be configured to effect an updating of the
classifications by directing a periodic rescan and reclassification
by all or some of the member devices.
[0023] Preferably, each device is user-controllable, using, for
example, a MAC-layer management entity (MLME) that is configured to
provide network control services. With regard to FIG. 1, in such an
embodiment, after joining or establishing a network, the device
waits for a command, at 130, then responds accordingly. If the
command is to repeat the channel search and classification, the
process loops to restart, at 110. If the command is to pair with a
specific target device, the process branches to establish the
pairing, at 145, discussed further below. Other commands are
executed as appropriate, at 160.
[0024] If, at 115, the device is a `paired` device, that is, a
device that is configured to communicate with a particular other
device or class of devices, in either a peer-to-peer or
master-slave pairing, the device searches the spectrum of channels
for the other/'target' device, as detailed further below.
[0025] If after a given number of tries, the device is unable to
locate its target pair device, the device is preferably configured
to actively advertise its presence, by either joining a discovered
network or by establishing its own network, at 125, discussed
above. If, on the other hand, the target device is found on a
channel, the devices establish the pairing on the channel at which
the target device is found, on an unused channel, or on a channel
having an existing network of secondary users.
[0026] The pairing of devices generally includes establishing a
secure and/or authenticated connection, via the exchange or
creation of session keys and other security measures, illustrated
in FIG. 1 as optional operations, at 150. Generally, the particular
protocol provides expected rules of behavior for paired devices,
such as a rule that requires a member of a pair to notify the other
member whenever the member is leaving a network, changing its
channel, and so on.
[0027] In a preferred embodiment, paired devices are also
configured to identify at least one backup channel, for use in the
event that communications are interrupted on their current channel,
due, for example, to the arrival of a primary user on the current
channel. Generally, one device identifies to the other device a
channel that it has found to be unused and of suitable quality. If
the other device also finds the channel to be unused and of
suitable quality, the identified channel is selected as the backup
channel; otherwise, the other device proposes an alternate channel
for consideration as the backup channel, and the process repeats.
One of skill in the art will recognize that although this
identification of a backup channel is particularly well suited for
seamless switching of paired devices, the principles provided
herein could also be applied for identifying a backup channel for
all of the members of a network to use, using the aforementioned
coordination and merging of channel classifications among the
members of each network.
[0028] As noted above, the device is preferably configured to
receive 155 and execute 160 commands that are either received
directly from a user interface to the device, or via a MAC-layer
management entity (MLME) or other network entity that is configured
to provide network control services.
[0029] FIG. 2 illustrates an example flow diagram for scanning and
classifying channels. The process starts at 210, corresponding to
the start of execution of block 120 in FIG. 1.
[0030] At 215, a channel is selected from among the available
channels in the spectrum, and a time-out timer is started. The
device monitors for the presence of discernable energy in the
selected channel, at 220.
[0031] Generally, the spectrum is identified as being allocated
among a variety of primary users, and the presence of a primary
user on a channel will exhibit distinguishable characteristics. For
example, television broadcasts conform to a given standard, and the
presence of carrier signals at particular locations within the
frequency band of the transmission, can be used to identify a
received signal as a television broadcast. A device that is
configured to operate as a secondary user of the spectrum is
preferably configured to recognize the distinguishing features of a
primary user. If these features are detected, the channel is
identified as being occupied by a primary user, at 240.
[0032] In like manner, a device that is configured to operate as a
secondary user will include an ability to recognize other secondary
users on the channel. For example, in accordance with WiMedia, as
defined in Multiband OFDM MAC Layer Specification by the WiMedia
Alliance, devices communicate using a MAC-layer "Superframe"
wherein each active device transmits a beacon during a beacon
period of the superframe, and each active device transmits data
during allocated times of a data/sensing/sleep period of the
superframe. A device that is configured to operate as a secondary
user using this protocol will be configured to recognize the
beacons of other secondary user devices. If the detected energy
corresponds to the defined characteristics of other secondary user
devices, the channel is identified as being occupied by secondary
users, at 230.
[0033] The energy detection period ends when either primary or
secondary users are detected, or when the aforementioned time-out
timer expires. Upon timeout, the received unrecognized energy is
assessed, at 250, to distinguish between an empty channel,
exhibiting relatively low received energy level, and an occupied
channel, exhibiting a relatively high received energy level.
Conventional thresholding techniques distinguish `high` and `low`
energy levels, typically based on a measure of accumulated energy
over the time-out period. If the energy level is low, the channel
is marked as clear, at 255; otherwise it is marked as being
occupied by an unknown user, perhaps another secondary user device
that is using an unrecognized protocol, at 260.
[0034] The classification of the selected channel is stored, and
the process is repeated for each of the other channels in the
spectrum until, at 270, all of the channels have been classified,
and the process is terminated, at 275.
[0035] FIG. 3 illustrates an example flow diagram for pair target
discovery. The process starts at 310, corresponding to the start of
execution of block 140 in FIG. 1.
[0036] If, at 315, the device is a master device of a master-slave
pair, it is configured to advertise its presence on a clear
channel, and wait for the slave/target device to find it. At 380,
the master device scans and classifies each of the channels, using,
for example the process of FIG. 2, discussed above. The master
device selects a clear channel, at 385, and transmits its beacon,
at 390. Alternatively, the master device may join an existing
network of secondary users, and transmits its beacon within that
network structure.
[0037] Unless otherwise directed, for example, via a user input or
a command from an MLME (not illustrated), the master device
continues to transmit its beacon until the slave device responds,
at 395. The search process then terminates, at 375, followed by a
pair connection process, discussed above with regard to block 145
of FIG. 1.
[0038] Otherwise, if the device is a slave device, or if the pair
is not a master-slave pair, the device is configured to alternately
search for the target device and advertise its presence for a given
number of iterations. The iteration count ('#Tries') is initialized
at 320 and incremented for each iteration at 325.
[0039] At 330, the device scans one or more channels, using a
modified form of the flow diagram of FIG. 2. In a preferred
embodiment, the scanning of channels will terminate as soon as the
target device is found. Also in a preferred embodiment, if a
primary user is located on a channel in a prior iteration, that
channel is not rescanned in subsequent iterations. If the target is
found, at 335, the search process terminates, at 375, and the pair
proceeds to establish a connection, as discussed above with regard
to block 145 of FIG. 1.
[0040] If the target device is not found, the searching device
selects a channel that is either clear or occupied by a network of
secondary users, at 340, and advertises its presence by
transmitting a beacon that includes its device identifier, at 350.
The device stays on the channel, advertising its presence, for a
period of time established by the timer loop 345-360. The timeout
duration is preferably set to assure that if the target device is
also searching for this device, the likelihood of discovery is
high. In a preferred embodiment, the minimum `stay-duration` is at
least as long as the maximum amount of time typically required to
scan each of the channels (hereinafter a `scan-duration`). To avoid
the possibility of both searching devices being `in sync`, scanning
and staying during coincident time periods, the stay-duration is
randomized. In a preferred embodiment, the stay-time is randomly
selected from a set of integer multiple of scan-durations; in a
straightforward embodiment, the stay-duration is set at either the
scan-duration or twice the scan duration, at 345.
[0041] If the target device responds to the searching device's
beacon, at 355, the stay-duration loop is terminated, the search
process is terminated, at 375, and the devices subsequently
establish pair-communication (145 of FIG. 1). Otherwise, at the end
360 of the stay-duration, the number of iterations is checked to
determine whether to quit the searching process, at 370. Generally,
if the target is not found within a given number of iterations, or
within a given amount of time, the searching device either joins an
existing network or establishes a new network, as discussed above
(125 of FIG. 1).
[0042] The choice of the number of iterations to use is generally
dependent upon the particular device. In a typical embodiment, a
portable device will be configured to repeat the pair-discovery
process of FIG. 3 at regular `wake-up` intervals, with a limited
number of iterations within the process, to conserve battery power.
Conversely, a plug-in device may continue the pair-discovery
process for an extended period, or even indefinitely.
[0043] One of skill in the art will recognize that variations of
the above processes are possible in view of this disclosure. For
example, if the devices of the pair are user-controllable, one
device may be set to act as a master device and stay on a selected
channel, even if the pair is not a master-slave pair, per se, while
the other device is set to search without staying on any channel,
for example by selecting a stay-duration of zero.
[0044] FIG. 4 illustrates an example system of dynamically
re-locatable secondary user devices (S) 400 operating in an
environment of primary users (P) 490. As discussed above, the
primary users 490 are generally the authorized and/or licensed
users of available channels in a spectrum, and the secondary
devices 400 are configured to avoid interfering with these primary
users 490 while also using channels in the spectrum.
[0045] An example block diagram of one of the secondary devices 400
is illustrated in FIG. 4. The example device 400 includes a
receiver 410 and detector 415 that are configured to monitor
selected channels for signal or energy content, under the control
of a controller 450. The channel classifier 420 receives the
measures of energy and/or other characteristics of the monitored
channel from the detector 415, and is configured to identify the
channels as being occupied or unoccupied; and, if occupied,
occupied by either a primary user 490, a secondary user 400, or an
unknown user (not illustrated). The determined classification is
stored in a memory 440. A decoder 460 is configured to process the
received signals on channels occupied by other secondary users, to
identify each other secondary user. The identity of each secondary
user on each secondary-user channel is also stored in the memory
440. The decoder 460 also decodes messages from other users after
communications are established on a selected channel.
[0046] The example device 400 also includes a beacon generator 425,
or other generator for generating an identifying signal that is
broadcast by a transmitter 430. The identifying signal is
transmitted on a channel selected by a channel selector 435, under
control of the controller 450, based on the classification and
other determined characteristics of the channels stored in the
memory 440. Messages 465 are transmitted after establishing
communication on a selected channel.
[0047] Preferably, the controller 450 is configured to control the
channel monitoring and beacon broadcasting consistent with the
example flow diagrams of FIGS. 1, 2, and 3, detailed above. Of
particular note, the controller 450 and channel selector 435 are
configured to avoid transmitting on any channel that is classified
as being occupied by a primary user, and, preferably, to avoid
transmitting on any channel that is classified as being occupied by
an unknown user. Preferably, the controller 450 also effects
communications with the other secondary users to update its channel
classifications based on classifications determined by the other
secondary users.
[0048] The foregoing merely illustrates the principles of the
invention. It will thus be appreciated that those skilled in the
art will be able to devise various arrangements which, although not
explicitly described or shown herein, embody the principles of the
invention and are thus within the spirit and scope of the following
claims.
[0049] In interpreting these claims, it should be understood
that:
[0050] a) the word "comprising" does not exclude the presence of
other elements or acts than those listed in a given claim;
[0051] b) the word "a" or "an" preceding an element does not
exclude the presence of a plurality of such elements;
[0052] c) any reference signs in the claims do not limit their
scope;
[0053] d) several "means" may be represented by the same item or
hardware or software implemented structure or function;
[0054] e) each of the disclosed elements may be comprised of
hardware portions (e.g., including discrete and integrated
electronic circuitry), software portions (e.g., computer
programming), and any combination thereof;
[0055] f) hardware portions may be comprised of one or both of
analog and digital portions;
[0056] g) any of the disclosed devices or portions thereof may be
combined together or separated into further portions unless
specifically stated otherwise;
[0057] h) no specific sequence of acts is intended to be required
unless specifically indicated; and
[0058] i) the term "plurality of" an element includes two or more
of the claimed element, and does not imply any particular range of
number of elements; that is, a plurality of elements can be as few
as two elements.
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